1. Field of the Invention
The present invention relates to a projection television and, more particularly, to a screen of a projection television having a high brightness.
2. Description of the Related Art
With the development of the information industry, there has been a need for an image display medium having a large screen. However, there is a technical limit in making a rectangular CRT of a television which has been a main conventional display device medium. Accordingly, to provide an image on a large screen, an image projection system in which a small CRT or LCD generates an image which is magnified by an optical lens to be projected on a large screen has been developed and widely used. The image projection system is known as a projection television or a video projector.
The image projection system can be divided into two types according to an image projecting method. One is a front projection system in which an image is directly projected on the front surface of a screen, and the other is a rear projection system in which an image is projected on the rear surface of a screen. The brightness of a display image of the rear projection system is much higher than that of the front projection system.
Referring to FIG. 1, a conventional projection television screen includes a Fresnel lens 11 for converting a divergent light beam from a projection lens (not shown) provided at a projection apparatus (not shown) into a parallel beam by receiving a light beam emitted from an image source (not shown) and deflecting the light beam so that an image is displayed at substantially uniform brightness throughout a wide viewing angle. A lenticular lens 12 is arranged close to the Fresnel lens 11 as a light spreading means for forming an image by spreading the parallel beam output from the Fresnel lens 11. The lenticular lens 12 is formed of a plurality of lens elements 13 having a column shape and arranged consecutively. A screen protective panel (not shown), which is formed of an acryl material, is provided on the front surface of the lenticular lens 12, that is, at the position facing a viewer. A protrusion 14 having a predetermined height is formed at a connection portion of each lens element at the front surface of the lenticular lens 12 contacting the rear surface of the screen protective panel, to absorb part of light divergently coming out of a bulged portion 13a of the lens element 13. A black strip 14a is coated in black ink at the end portion of the protrusion 14. Thus, the contrast of an image formed on the front surface of the lenticular lens 12 can be improved.
FIG. 2 is a cross sectional view of the Fresnel lens 11 shown in FIG. 1, vertically crossing the center of the Fresnel lens 11. Referring to FIG. 2, the shape of a surface facing the lenticular lens 12 has a saw-toothed shape. FIG. 3 shows a magnified portion of a circled portion A in FIG. 2. Referring to FIG. 3, part of incident light, in particular a light beam 22 input at an angle greater than the critical angle of the total internal reflection of a sharp portion 20 of a sawtooth, cannot pass through the Fresnel lens 11 due to the total internal reflection. If the light cannot pass through the Fresnel lens 11, and proceeds in a direction totally different from the originally set direction after the total internal reflection, it cannot be used in image projection.
In the above conventional screen, the efficiency of light passing is lowered due to loss of light at the Fresnel lens so that the entire brightness of the screen is lowered.
To solve the above-described problems, it is an aspect of the present invention to provide a projection television screen having a high brightness by minimizing loss of light due to the shape of the surface of the Fresnel lens.
To achieve the above aspect, there may be provided a screen of a projection television comprising a Fresnel lens for converting an incident light beam emitted from an image source into a parallel beam, a lenticular lens formed by sequentially arranging a plurality of lens elements having a column shape parallel to one another for forming an image from the parallel beam output from the Fresnel lens and spreading the formed image, and a protective panel installed on the front surface of the lenticular lens for protecting the lenticular lens. The Fresnel lens may comprise a base substrate and a lens unit contacting one side of the base substrate, patterns having a saw-toothed shape formed on a surface of the lens unit facing a lenticular lens, and a portion of each pattern corresponding to a sharp portion of a sawtooth may have a processed curved surface having a predetermined curvature.
In the present invention, the refractive indexes of the base substrate and the lens unit may be different from each other.
In the present invention, the curved surface may be a spherical surface or an aspherical surface.
Thus, by using the screen of the projection television according to the present invention, the brightness of the projection television can be improved and the brightness can be uniformly distributed throughout the entire screen.